From Sajun.org


An (N,M,D,K,e)-extractor is a bipartite graph with N nodes on the left and M nodes on the right such that each node on the left has D neighbors (on the right), which has the added property that for any subset A of N of size at least K, choosing a random node in A and then following a random edge brings you to a node x on the right side with probability within e of the uniform distribution.

These graphs are called "extractors" because they can be used to "extract" randomness from weak random sources.


An extractor is a holding device, that holds onto the rim of ammunition, as to eject the empty casing when cycling after a shoot has been fired. Extrators can be found on bolt action, lever-action, semi-automatic and fully automatic firearms.